Tuberculosis, once the “white plague,” is no stranger to anyone. But there is another disease that is increasingly being mentioned that is very similar to TB, and that is non-tuberculous mycobacterial disease. Now, let’s understand a few common questions about nontuberculous mycobacterial disease. I. What are nontuberculous mycobacteria? Nontuberculous mycobacteria are mycobacteria other than Mycobacterium tuberculosis and Mycobacterium leprae, and although they have been recognized for only six decades, more than 160 species have been identified. The vast majority of nontuberculous mycobacteria do not cause disease, such as Mycobacterium gordonii, Mycobacterium incidentalis, and Mycobacterium hyopneumoniae, especially when isolated from sputum, urine, and stool specimens, often due to specimen contamination. There are only a dozen non-tuberculous mycobacteria that commonly cause disease, including Mycobacterium intracellulare, Mycobacterium abscessus, Mycobacterium kansasii, and Mycobacterium avium. The morphology of nontuberculous mycobacteria under the microscope is very similar to that of tuberculosis, and routine antacid staining or culture cannot identify tuberculosis and nontuberculous mycobacteria, and further molecular biology or biochemical tests are required to distinguish them. II. What is non-tuberculous mycobacteriosis? Non-tuberculous mycobacteria are widely found in tap water and soil, and everyone has the opportunity to come into contact with them, but their ability to cause disease is very weak, and the vast majority of people do not get sick after contact. Most people with nontuberculous mycobacterial disease are immunocompromised, such as those who have had previous lung disease, AIDS patients, and organ transplant patients, and a few have no significant immunodeficiency. Nontuberculous mycobacteria can cause damage to organs such as the lungs, lymph nodes, skin and soft tissues, joints, and in severely immunodeficient populations can also cause disseminated lesions. Unlike tuberculosis, nontuberculous mycobacteriosis is not an infectious disease, and so far there is no evidence of human-to-human transmission. With the gradual control of the TB epidemic, the number of patients with nontuberculous mycobacterial disease detected each year has exceeded the number of patients with TB in the United States since the 1980s. In recent years, nontuberculous mycobacterial disease has received increasing attention from scientists for two main reasons: first, the improved level of tuberculosis laboratories and the increased level of awareness of nontuberculous mycobacterial disease among physicians has led to the identification of more and more patients with nontuberculous mycobacterial disease; second, the emergence of a severely immunosuppressed population due to AIDS, organ transplants, and the use of immunosuppressive drugs. They are more vulnerable to opportunistic pathogenic bacteria including nontuberculous mycobacteria. It can be said that nontuberculous mycobacterial diseases are diseases that have only been gradually recognized with technological advances, and their discovery has brought new challenges to medical research. III. Is non-tuberculous mycobacteria found in sputum non-tuberculous mycobacteriosis? How can I diagnose nontuberculous mycobacteriosis? Since most nontuberculous mycobacteria do not cause disease, the discovery of nontuberculous mycobacteria in sputum specimens requires further examination to identify the type of nontuberculous mycobacteria and to assess the likelihood of bacterial pathogenicity, which is a basic prerequisite for the diagnosis and treatment of nontuberculous mycobacteriosis. It is currently believed that patients must fully meet at least the bacteriological and imaging criteria for nontuberculous mycobacterial lung disease in order to be diagnosed with nontuberculous mycobacterial lung disease, where sputum examination requires that the same nontuberculous mycobacteria be found at least twice, which means that patients need to have sputum examined multiple times. There are several steps in diagnosing nontuberculous mycobacterial lung disease: first, to identify the kind of nontuberculous mycobacteria, which is now generally done by molecular biology, second, to determine whether the bacteriological criteria for diagnosing nontuberculous mycobacterial lung disease are met, and finally, to determine whether the clinical criteria for nontuberculous mycobacterial lung disease are met by a comprehensive analysis. The isolation of nontuberculous mycobacteria from sputum specimens only once does not necessarily mean that the patient has nontuberculous mycobacteriosis. 4. Does nontuberculous mycobacteriosis require treatment? The cure rate for tuberculosis is 95%, and the cure rate for nontuberculous mycobacterial lung disease is comparable only to that of Mycobacterium kansasii lung disease; most nontuberculous mycobacterial diseases have poor outcomes. The cure rate of intracellular mycobacteria and Mycobacterium avium pneumonia is about 60%, and the cure rate of Mycobacterium abscessus pneumonia is only 30%. On the other hand, patients with immunocompetent nontuberculous mycobacteriosis progress slowly compared with those with tuberculosis. Therefore, not all patients with nontuberculous mycobacteriosis should receive anti-mycobacterial therapy. Before treatment, physicians need to weigh whether patients will benefit from treatment. The choice of whether to treat should take into account the type of bacteria isolated, the patient’s age and underlying disease, and the characteristics and extent of the lesion, and evaluate the potential risks and possible benefits of treatment. In general, patients with isolation of virulent bacteria (Mycobacterium kansasii, Mycobacterium intracellulare, Mycobacterium abscessus) with a clinical type of cavitation and relatively rapid disease progression should be considered for treatment. There are several interventions for nontuberculous mycobacteriosis as follows: 1. Chemotherapy. It is the most commonly used intervention modality with good efficacy in intracellular mycosis, Mycobacterium avium and Mycobacterium kansasii disease; 2. Surgical treatment. Limited to patients with limited lesions and failed chemotherapy; 3. Symptomatic support. Treatment such as cough suppression and sputum reduction can be given to alleviate patient symptoms in patients who have failed treatment or are at high risk of adverse drug reactions. Nontuberculous mycobacteriosis is a disease that is gradually being taken seriously with technological advances. Standardized diagnosis and rational treatment can improve the quality of life of patients and enable them to benefit from appropriate interventions.